A wire electric discharge machining method is a known method for cutting a workpiece (product to be machined). In the wire electric discharge machining method, in a state where an electrode wire for electric discharge machining formed of a wire pierces a workpiece immersed in a machining fluid, a voltage is applied between the electrode wire and the workpiece to generate electric discharge, the workpiece is melted by using heat generated by the electric discharge, and a melted portion of the workpiece is removed by vaporization and explosion of the machining fluid. The workpiece is moved in left and right directions and in forward and backward directions to continuously cause the melting and the removing phenomena along the trajectory of the electrode wire on the workpiece, thereby achieving cutting so as to have a desired shape.
The smaller the wire diameter of an electrode wire for electric discharge machining, the higher the precision of the machining that can be realized. Therefore, in general, a reduction in the diameter of the electrode wire has been desired. On the other hand, tension is provided to the electrode wire so that the electrode wire is not bent during electric discharge machining. When the diameter of an electrode wire is decreased, the electrode wire cannot withstand the tension and becomes easily broken. Therefore, it is also necessary to ensure a certain degree of tensile strength of the electrode wire.
Accordingly, as described in PTL 1, an electrode wire for wire electric discharge machining has been developed in which a surface of a steel wire serving as a core wire of an electrode wire is plated with a copper-zinc alloy (brass). Such an electrode wire includes a core wire formed of a steel wire and thus is excellent in terms of tensile strength compared with a brass wire and the like. Furthermore, a conductive property is ensured by copper in the brass plating, and discharge performance is ensured by zinc in the brass plating.